Inpatient normal volunteers ate 6 eggs daily while taking diets rich in saturated or unsaturated fat. The plasma cholesterol concentrations increased transiently with both types of fat, but the greatest increase occurred with saturated fat. In the high density lipoproteins of all subjects, a subfraction developed an increased content of apolipoprotein E. The type of dietary fat did not appear to influence the amount of this apo-E containing HDL. The apo-E HDL was able to bind to cells in tissue culture and compete with low density lipoproteins.